To demonstrate simultaneous multispectral detection, short and long wavelength thin-film detectors, which are grown and optimized separately, are collocated and heterogeneously integrated in a three-dimensional (3-D) stack onto pads on an Si substrate. Simultaneous two-color detection by each detector in the 3-D stack has been measured and theoretically explored. This heterogeneous integration of two different detectors in a 3-D stack is an interesting physical integration technology for multispectral imaging systems and coarse wavelength-division-multiplexing systems.